Prototyping is often used during product development to verify design concepts and to facilitate advance testing. A prototype must have characteristics sufficiently close to the desired product to permit a realistic prediction of actual product performance. Prototyping molded parts can be expensive both in capital outlay and in development time. Production quality molded parts are generally produced using metal mold manufacturing. A metal mold is expensive to produce and can require a long lead time, as time must be allocated for designing the mold, machining the mold cavity, texturing the surface of the mold cavity, and the like. When the number of design iterations is considered along with the relatively small prototype volumes and high cost of metal mold development, it is clear that metal mold manufacturing is not well-suited for many prototyping applications. Similarly, metal mold manufacturing would not be suited for short cycle time, low volume production runs. Alternatives more suitable for prototyping and low volume production have been explored. These alternatives include room temperature vulcanization (RTV) molds, and spray metal molds.
A typical RTV design involves forming a mold from a pliable material, usually urethane, silicone, or similar elastomeric resin which can be cured at or near room temperature. First, a model of the part, often called a master, is formed using a stereolithography apparatus (SLA) process, or other suitable technique. Typically, the master is designed using a computer aided design (CAD) system which can generate data needed to construct the master. This CAD data is used by the SLA process which uses a laser to cure a photopolymerizable resin to produce a solid three-dimensional object. Although an SLA master is suitable for cosmetic analysis of the part, such as fit and form, and for some analysis of functionality, the SLA master may not be suitable for full mechanical testing. The materials currently adaptable to the SLA process usually have unacceptable mechanical properties for many applications, such as the inability to withstand high mechanical stresses. Next, the part is encapsulated with a material suitable for use in a RTV process. The material is then cured to form a RTV mold in which duplicates of the master are cast from a urethane, epoxy, or similar resin, which cross links at temperatures at or near room temperature. RTV molds can support materials which have properties, such as impact strength, that are better than the materials which can be used to produce the SLA master. However, parts cast in RTV molds lack the stiffness, impact and temperature performance, and other mechanical properties obtainable from injection molded plastics, such as polycarbonates and the like, which are typically used in production quality parts. Thus, a part produced using a RTV mold does not provide an adequate representation of the final product for true mechanical testing and product evaluation.
Spray metal molds also require a master. A spray metal mold is formed by an application of metal spray to the master which forms a hardened shell which assumes the shape of the part. The shell is reinforced with a support base before being used as a mold. A spray metal mold can support a wider variety of materials than a RTV mold. However, a spray metal mold for a part having intricate details may have multiple segments, called inserts, to accommodate oddly shaped features of the part. As the level of detail increases, the cost and lead time required for a spray metal mold may approach the cost and lead time of a conventional prototype metal mold.
Manufacturers are continuously seeking reductions in the length and cost of the product development cycle. Rapid prototyping and low volume production are useful tools in this effort. Current techniques for prototyping molded parts are costly and inadequate for many applications. Hence, there is a need for a more expeditious and cost effective process for producing molds.